Ariel Zambelich for The Wall Street Journal Jon Quisenberry of Bradford Farms -- a genetic breeder -- picks samples of interspecific plums from the trees at Kingsburg Orchards in Kingsburg, Calif., to be tasted for specific qualities, such as flavor, size and production value.

Although every living thing eventually goes extinct in the face of changes ranging from ice ages to interspecific competition, the fossil record shows that while some species debut and are booed off the stage, there are others -- cockroaches and sharks come to mind -- whose dance with time is more waltz than jitterbug.

This literature shows that symbiogenesis, interspecific fusions (hybridogenesis, gene transfers of various types, karyotypic fissioning, and other forms of acquisition of "foreign genomes" or epigenesis) are more important than the slow gradual accumulation of mutation or sexual mergers.